Spray metal process for making precision articles



July 1950 A. G. CRAIG 2,944,338

SPRAY METAL PROCESS FOR MAKING PRECISION ARTICLES Filed Dec. 30, 1953 Inventor Allen G. Craig, W 3 woma- His Alibovney.

United States Patent SPRAY METAL PROCESS FOR MAKING PRECISION ARTICLES Filed Dec. 30, 1953, Ser. No. 401,273

3 Claims. (Cl. 29-423) This invention relates to a spray metal process for making precision articles and more particularly to a spray metal process for making articles such as wave guides requiring sharp and well-defined inside surfaces, precision molds, and precision punches and dies. 7

Wave guides of the type used in radar plumbing systems must have sharp and well-defined inside surfaces. Also, it is frequently desirable that such radar wave guides have sharp curvatures with short radii. Because of these requirements it has been the practice in the past to make wave guides frorn wrought metal. However in many instances special techniques and expensive equipment must be used in order to twist and shape the metal to meet the precise requirements needed in the finished product. 7

Precision molds for castings have often in' the past required expensive and complicated, equipment for their fabrication. The problems of economy and durability have been aggravated when the molds are used for high temperature castings.

In the making of precision punches and dies for press forming production parts, high strength materials, such as steel alloys, have proven to be the most durable. However, for many operations the cost and length of time required to make steel punches and dies prohibits their use and an inferior substitute material has been used.

It is accordingly one object of this invention to provide a spray metal process for making precision articles requiring sharp and well-defined surfaces.

Another object of the invention is to provide a simple and economical process for making precision articles.

Another object of the invention is to provide a spray metal process for making precision articles wherein reinforcing members are incorporated in the spray metal structure.

Another object is to provide a spray metal process for making precision articles wherein cooling coils are incorporated into the article to facilitate cooling of the article during its use.

Briefly stated, in accordance with one aspect of this invention, a matrix or pattern of a predetermined shape is formed from a suitable disposable material. A thin coating of suitable metal is then applied to the matrix by metal spraying. Reinforcing members, for example, piano wire or other material having high tensile strength, are placed on the coating and-additional metal is sprayed over the reinforcing members to form a spray metal structure of sufiicient thickness to be self-supporting. When it is desirable, cooling coils for circulation of a coolant may also be incorporated into the spray metal structure. The disposable matrix or pattern may then be removed from the spray metal structure.

The invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Fig. 1 is an elevation, partly in section, of a portion of a wave guide and a wave guide termination used for test purposes, and the process for making same, illustrating one embodiment of the invention.

Fig. 2 is a view showing a section taken along lines 2-2 of Fig. 1.

Fig. 3 is a view showing a section of a precision mold and the process for making it in accordance with the teachings of this invention.

Fig. 4 is a view showing a section of a precision punch and the process for making it in accordance with the teachings of this invention.

Fig. 5 is an elevation, partly in section, of the finished punch.

Referring more particularly to the drawings, a wave guide 10 and a wave guide termination 11 may be seen in Figs. 1 and 2 as formed by spraying metal on a disposable core 12. The disposable core 12 is made from a disposable material, such as Woods metal, wood or plastic into a shape conforming to the desired internal shape of the wave guide and termination. The core 12 is preferably carefully cleaned immediately prior to spraying, for example, by very light blast cleaning or vapor-degreasing. A thin coating of molten metal is then sprayed directly onto the disposable core to a thickness suflicient to make a conductive coating 13. This thickness may be as little as .00001 inch or even less. That such thickness is satisfactory is' believed to be due to the nature of the conductivity along the coating surface which is according to the well known skin effect. This spraying may be accomplished by the use of a suitable spray gun. The metal sprayed on the core should be electrically conductive and may be steel or its alloys, or non-ferrous materials, depending on the service intended and the melting point of the molten metal. Silver is an admirable metal for use in the making of a wave guide since silver is a good conductor and since it is well-suited for the metal spraying process.

The termination 11 in its use for testing purposes, and also portions of the wave guide itself, may be subjected to considerable stresses and also to high temperatures. This is true because in testing operations, the termination and the end portions of the wave guide must absorb all the energy normally transmitted through the wave guide and out through a lens. In radar systems such energy is partly electrical, partly mechanical and partly heat energy, hence the stresses and-high temperatures. To strengthen the wave guide and termination, reinforcing members 20 having high tensile strength are placed on the coating 13. The melting point of the reinforcing members 20 is preferably higher than that of the spray metal because otherwise the reinforcing members may melt entirely, or in part, and lose their strengthening characteristics. However the spray metal is not necessarily in an entirely molten condition and reinforcing members may be used which do not substantially melt upon contact with the spray metal, even though the melting point of the reinforcing members is close to or even less than that of the spray metal. Piano wire, for example, has been found to be one suitable type of reinforcing member. I

In order to provide for the dissipation of the high temperatures which may be generated within the wave guide and termination, cooling coils may be built in. Such a cooling coil 21 may be placed on the coating 13 in a suitable fashion, for example, by winding it around the coating leaving inlet and outlet portions of the coil exposed for the circulation of a suitable coolant. Additional layers are then built up to form a strengthening backing 15 for the coating and to secure the reinforcing members 20, and the cooling coil 21 to the coating 3 13 by metal spraying, e.g., by the use of a spray gun 14. These additional layers complete an integral selfsupporting spray metal structure and may be of a relatively, inexpensive backingrnaterial, for example, copper, zinc or ferrous alloys. The thickness of the backing 15 may be as much-as one-eighth of an inch using presently known spraying techniques and metals. However, as these techniques are improved, greater thicknesses may be practical.

After the spray metal structure of the wave guide 10 and the wave guide termination 11 has been built up as described above to the desired thickness, which is a thickness enabling the structure to be strong and selfsupporting, the disposablecoreis removed. :In the event Woods metal has been used as the disposable material, the structure may be placed in boiling water and the Woods metal melted out. If wood has been used as the disposable material, it may be chipped out, and if a plastic material has been used, it may be dissolved by solvents, or warmed and removed. Upon removal of the disposable core an inside facing is left which with a, minimum of grinding provides a very accurate, economical and serviceable wave guide and wave guide termination surface.

Fig. 3 illustrates another embodiment of this invention as used in the making of high strength molds for use in high temperature castings. As described in con nection with Figsal and 2, a disposable core or matrix 30 may be formed of a disposable material and having a shape conforming to the shape of the desired cast product. A thin spray metal coating 31 may be built up by metal spraying onto the matrix 30. The melting point of the metal used in spraying must be higher than that of the casting material to be cast. Molybdenum and tungsten are examples of high temperature metals which are suitable for spraying. This coating 31 need be only as thick as is required to withstand the high temperatures of the molten cast metal, and since it is usually sprayed with a relatively expensive metal, it is preferably extremely thin. Reinforcing members 20 and a cooling coil 21 may then be placed on the spray metal coating as described hereinabove, and additional layers of a relatively inexpensive backing metal may then be sprayed over the structure 31, the reinforcing members 20, and the cooling coil 21 to secure the members. and coils to the coating and form an integral self-supporting spray metal structure 32. Upon removal of the disposable core, a high strength mold is left capable of handling high temperautre castings, as they may be cooled by circulating cooling fluid such as water through coil 21.

Figs. 4 and 5 illustrate a further embodiment of this invention as used in making punches. A matrix or negative 40 is made up from an existing mock-up. This matrix again may be made of a disposable material, such as metal, plastic, wood, or plaster. The matrix is then metal sprayed with a wear or abrasion resistant metal, such as high carbon steel or molybdenum, to form-a thin coating 41. This coating 41 need be only thick enough towithstand the wear to which the punch is subjected, and for many purposes may be quite thin. For example, where a punch will be used for only a few hundred punchings, an extremely thin coating of the more expensive, wear resistant metal will satisfactorily withstand the wear and impact stresses. Reinforcing members 20 may be placed on the coating 41 as in previously described embodiments or may be tacked for temporary holding purposes, and additional layers of relatively inexpensive backing metal may be sprayed on the coating 41 covering the reinforcing members and securing them to the coating to form an integral self-supporting spray metal structure 42. The cavity thus formed may then be filled up with a material 43 (see Fig. 5) having sufiicient compressive strength, for example, metal, concrete, plastic, or plaster, as the application may require. Upon removal of the structure thus formed from the disposable matrix 40 and with a minimum of finishing, a high strength, economical punch is formed.

While particular embodiments of my invention have been illustrated and described, modifications thereof will occur to those skilled in the art. It is, therefore, to be understood that the invention is not limited to the particular arrangements disclosed, and that the appended claims are intended to cover all modifications which do not depart from the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A spray metal process for making a hollow article.-

requiring sharp and well-defined surfaces and capable of withstanding high temperatures comprising, forming a core of disposable material having a shapfi conforming to that of the article desired, metal spraying a coating onto said core, placing coilingcoils on said coating, metal spraying additionallayers onto said core and coils to secure them to the coating and form an integral spray metal structure of sufiicient thickness to be self-supporting, and removing said disposable core from the spray metal structure.

2. A spray metal process for making a strong hollow articlerequiring sharp and well-defined inside surfaces and capable of withstanding high temperatures comprisin'g, forming a core of disposable material having a shape conforming to the shape of the inside surface of the desired article, metal spraying a coating onto said core, adding reinforcing members to said coating, placing cooling coils on said coating, metal spraying additional layers onto said coating, reinforcing members, and coils to form an integral spray metal structure of sufiicient thickness to be self-supporting, and removing said disposable core from the spray metal structure.

3. A spray metal process for making a mold capable of withstanding high temperatures and high stresses comprising, forming a matrix of disposable material, metal spraying a coating onto said matrix, placing cooling coils on said coating, placing reinforcing members on said coating, metal. spraying layers of a second metal onto said coils and reinforcing members to secure them to the coating and form a rigid integral structure, and removing said disposable matrix from said structure.

References Cited in the file of this patent UNITED STATES PATENTS 1,179,762 Schoop Apr. 16, 1916 1,243,654 Clark Oct. 16, 1917 1,790,213 Gwaltney Jan. 27, 1931 1,940,814 Saeger Dec. 26, 1933 1,969,540 Bergstrom Aug. 7, 1934 1,994,767 Heintz Mar. 19, 1 935 2,172,604 Blackburn Sept. 12, 1939 2,250,246 Axline July 22, 1941 2,390,183 'Seligrnan Dec. 14, 1 945 2,499,977 Scott Mar. 7, 1950 2,583,533 Hiensch Jan. 29, 1952 2,592,614 Stoddard Apr. 15, 1952 

